CHAP. VII. } MAMMALIA OF THE NEW WORLD. 139 
and Upper Eocene, no remains of this order have been found; 
and in 1869, Dr. Leidy remarked on the small average size of 
the extinct North American mammalia, which were almost all 
smaller than their living analogues. Since then, however, won- 
derful discoveries have been made in deposits of Middle Eocene 
age in Wyoming and Colorado, of a group of huge animals not 
only rivalling the elephants in size, but of so remarkable and 
peculiar a structure as to require the formation of a new order of 
mammals—Dinocerata—for their reception. 
This order consists of animals with generalised Ungulate and 
Proboscidean affinities. The lower jaw resembles that of the 
hippopotamus ; they had five toes on the anterior feet and four on 
the posterior ; three pairs of horns, the first pair on the top of the 
head, large and perhaps palmated, the second pair above the eyes, 
while the third and smallest stood out sideways on the snout. 
They had enormous upper canines, of which the roots entered 
the middle horn cores, no upper incisors, and small molars. 
Professor Marsh believes that they had no trunk. The remains 
discovered indicate four genera, Dinoceras (3 sp.), Tinoceras 
(2 sp.), Uintatherium (1 sp.), and Hobasileus (2 sp.). Many other 
names have been given to fragments of these animals, and even 
those here given may not be all distinct. 
Another new order, Tillodontia, recently established by Pro- 
fessor Marsh, is perhaps yet more remarkable in a zoological 
point of view, since it combines the characters of Carnivora, 
Ungulata, and Rodents. These animals have been formed into 
two families, Tillotheride and Stylinodontide; and three genera, 
Tillotherium, Anchippodus, and Stylinodontia. All are from the 
Eocene of Wyoming and New Jersey. Perhaps to these must be 
added Elotherium from the Miocene of Dakota, the other forms 
being all Eocene. They were mostly animals of small size, 
between that of the capybara and tapir. The skull resembled in 
form that of a bear ; the molar teeth were of Ungulate type, and 
the incisors like those of a Rodent; but the skeleton was more 
that of the Urside, the feet being plantigrade. Professor Cope 
has since described three new genera from the Eocene of 
New Mexico, Ectoganus, Calamodon, and Esthonyr, comprising 
